1. Technical Field of the Invention
The present invention relates to mobile cellular telephone communications systems and, in particular, to a system and method for forwarding calling party information to a mobile terminal user without invoking a trunked connection.
2. Description of Related Art
Historically, paging systems and mobile telephone systems have provided service to a limited geographic area using a relatively high-powered centralized transmitting site. This arrangement has worked well in small cities and municipalities, but has often proved unsuitable for large metropolitan areas. To adequately serve a large geographic area, cellular phone systems began to simulcast (transmit the same signals at substantially the same time) from several transmitters strategically positioned to provide wide-area coverage. In such systems, a pager or a mobile station could receive information anywhere in the specified wide area.
Today, the trend in wireless communications is to provide even greater geographic coverage. Nationwide communication systems are often contemplated in an attempt to provide communication services to customers without regard to where they are in the United States, or for that matter, in the world. One known communication system employs satellites to transmit paging messages to pagers as well as cellular mobile stations.
It is well known that, in ground-based cellular communication systems or satellite-based communication systems, signal path interference can block a signal and prevent it from reaching the specified receiver. Such signal path interference of this type is often due to structural blockage from thick foliage, buildings and the like. Generally speaking, the signal path interference results in a mobile station being in an operational mode but also being temporarily unable to communicate with a transceiver.
Many methods and systems have been proposed for ground-based as well as satellite-based communication systems in response to the problem of mobile station unavailability for message delivery due to signal path interference as set forth in U.S. patent application Ser. No. 08/719,282, entitled "Subscriber Feature Controlled High Penetration Messaging", filed Sep. 24, 1996, of which applicant is a co-inventor. One proposed system includes a store in a mobile switching center for storing a message until the presence of the mobile station is detected through a registration, at which point the message is delivered or made available for retrieval. A drawback to this approach, however, is that the delivery of important messages may be unacceptably delayed until the mobile station clears the signal interference and re-registers within a cell area. Another drawback is that there are no further attempts by the mobile switching center transceiver to communicate with the mobile station and deliver the potentially important message until re-registration occurs.
Another proposed solution to the problem of mobile station unavailability owing to signal path interference is to increase the transmission power level within a "standard" range of power levels. Increasing the power level within a standard range, however, may not be sufficient to overcome the signal interference due to structural path blockage. Moreover, current proposals for increasing transmission power include increasing power either on a system wide basis or on a cell wide basis. Under these proposals, unnecessary power levels are utilized for transmission to mobile stations which are receiving signals clearly in order to reach those mobile stations that are not receiving signals clearly.
In proposed satellite-based communications systems, a mobile station located toward the center of a building or under a large oak tree with thick or wet foliage may be subject to signal path interference and may not be able to receive and respond to a message delivery attempt or to a paging attempt from a satellite-based transceiver. With satellites, the solution of transmitting at increased power levels is not always possible because many satellites have fixed transmission power level capabilities. While some satellites can exceed the standard transmission power levels to attempt to deliver a message, or to page a mobile station, other satellites have no capability of transmitting at increased power levels. Thus, a given satellite serving the mobile station may not be capable of performing a high power level transmission to overcome signal path interference.
Even for those scenarios in which it is possible to exceed standard transmission power levels, economic disincentives exist for doing so. It is likely that only some users will be interested in selectively using a higher power transmission level service. Other users simply may not care about becoming more "reachable". It would be unfair for the expenses of increased power transmission levels to be borne by all mobile station users. Thus, even if a satellite-based transceiver has the capability to transmit a message at an increased power level, the increased power level should not be provided to those users that would not ordinarily need or appreciate such a service feature.
Timing problems also exist with using satellite-based transceivers for increased power transmissions to a ground-based receiver. First, in order to avoid unnecessary transmissions at high power levels, increased power level transmissions should only be made after a transmission at a standard power level fails. Second, in a typical communication system, namely one in which high penetration power level transmissions do not occur, a paging system may designate that a user is unavailable after a mobile station fails to respond to at least one page attempt. In conventional systems, certain time out values are established which only account for the amount of time required to page a mobile station at a standard power level. Conventional systems are set up wherein an originating source of a message rebroadcasts its message to initiate paging once a time out value is reached. Unfortunately, such timeout values are frequently less than the time required for the communication system to initiate and process a second paging attempt or a third paging attempt at higher power levels.
In view of the aforedescribed difficulties, assignee developed a system and method for reducing unnecessary broadcast or paging attempts, as set forth in more detail in said co-pending patent application, where the link margins or effective signal strength of a transmission may be inadequate for the mobile station or terminal to "hear" a page request. Through a high penetration notification (HPN) message, however, the terminal may be able to hear the page request at a higher power level. The page request may contain information, such as part of a Short Message, the Calling Party Number for terminating calls, etc. Receipt of such a notification informs the mobile terminal user of the attempt to communicate, and that, if they move into better radio coverage, the short message can be re-sent or they can call back the caller.
One problem with the aforedescribed HPN technique, however, is that elaborate system services are invoked whether or not the called mobile terminal user is attached to the cellular-based or satellite-based network. In particular, in the HPN system of the co-pending patent application, a mobile switching center (MSC) in the cellular network, when asked to provide a roaming number (identification), may override a detach marking associated with a particular user and return a roaming number anyway, e.g., the last number used by that subscriber. One consequence of this overriding, however, as discussed in more detail hereinafter, is that triggering of supplementary services for unavailable subscribers is suppressed in the MSC and seizure of a trunkline occurs for the purpose of delivering the calling party identity, an event wholly unnecessary when the called party is detached from the system.
It is, accordingly, a first object of the present invention to eliminate such unnecessary system actions.
It is also an object of the present invention to provide a system and method for improved high penetration notification for use in both terrestrially-based and satellite-based systems.